NBSIR 74-434

Test and Evaluation of Baby Walkers

and Walker-Jumpers

Daniel J. Chwirut

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

May 1974

Final Report

Prepared for

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

NBSIR 74-434

TEST AND EVALUATION OF BABY WALKERS

AND WALKER-JUMPERS

Daniel J. Chwirut

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D,C. 20234

May 1974

Final Report

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

X

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Test and Evaluation of Baby Walkers and Walker-Jumpers

Daniel J. Chwirut

ABSTRACT

Accident reports from hospital emergency

rooms were surveyed to determine the probable

causes of accidents involving baby walkers and

walker-jumpers. Test methods were developed to

simulate service conditions to determine if the

characteristics leading to accidents are present in all or only a few of the items on the

market. These test methods include tests for

dynamic and static stability, step roll-over

stability, plastic bead strength, durability,

and location of scissor joints. The test

methods and performance criteria are intended

to supply information leading to federal safety

standards

Key words: Accident reports: baby walkers;

infants; safety standards; test methods;

walker-jumpers.

1. INTRODUCTION

Accident reports received through the Bureau of Product Safety (now

part of the Consumer Product Safety Commission) listed many injuries,

mostly lacerations, abrasions, or fractures in the face, head, and

shoulder areas, to 7-14 month-old children as a result of accidents involving baby walkers and walker-jumpers. Most injuries resulted from

the walker tipping over after being run into a stopping mechanism, such

as carpet molding, gravel, raised concrete, floor heating vents, and door

sills. Other accidents involved the walker being run over a step or down

a flight of stairs, and finger lacerations caused by "scissor" joints.

An investigation was undertaken to determine what characteristics of the

walkers possibly led to the accidents, to determine if these characteristics were inherent to all or only a few of the items on the market, and

to determine appropriate test methods and performance criteria so that

federal safety standards could be written. Situations investigated included dynamic stability (moving walker runs into a stop), static

stability (stopped walker is tipped over by a standing child), stability

when running over a single step, location of scissor joints relative to

child sitting in jumper, strength of plastic beads within reach of child's

mouth, and durability.

1
2. TEST PROGRAM AND RESULTS

2.1 Dynamic Stability

Since the majority of the accidents involved the dynamic stability

of the walker, the first and largest effort was directed toward understanding this problem.

If the walker is considered to be a rigid system (i.e. frame

deflections, spring extensions, etc. are neglected), the mechanics of

the event of the walker hitting a stop are straightforward. For the

walker to tip over, the kinetic energy before impact must be greater

than the energy required to rotate the walker to the unstable equilibrium

position (see fig. 1), or mathematically,

|i > [l2 + h2]^2 - H,

where V is velocity, g is the acceleration due to gravity, and L and H are the horizontal and vertical dimensions from the axis of rotation to

the center of gravity. On a horizontal surface, the velocity is fixed by

the capabilities of the user, so the stability of the walker is determined by the location of the center of gravity.

To get some indication as to the speeds attained by children in

walkers, two 10 month old "volunteers", a 22 lb* (10 kg) and an 18 lb

('6.2 kg) female, were timed while using walkers in the laboratory. Both were allowed to move over an unobstructed course, with enticement from

parents (see fig. 2), in a variety of walkers, including their own. Times to traverse 5-ft (1.5-m) distance markings were taken to determine

some rough indication of maximum speed. One child achieved a maximum

speed of 2.5 feet per second (0.76 m/s), and the other A feet per second

(i.2 m/s). Parents of both indicated that it seemed that the children

went faster at home in their natural environment. Another important

observation was that both children achieved maximum speed going backwards.

This seems logical since it appears to be easier for a child to sit and

propel himself backwards than to stand and run forward. This is

significant since the center of gravity of most walkers is closer to the

back wheels than to the front.

Based on the speeds measured and the comments that the children may

go faster at home in their own surroundings, it was decided to test at

speeds of 4 and 6 feet per second (1.2 and 1.8 m/s). The walkers were

tested in forward, backward, and sideways orientations, and impacted

obstructions 0.25, 0.50, and 1.0 in (0.6, 1.3, and 2.5 cm) high.

*Units for physical quantities in this paper are given in both the U. S.

Customary Units and the International System Units (SI)

2
These obstructions were intended to simulate carpet molding, door sills,

or other raised obstructions. A plastic doll, approximately the size of

a 1 year old child, was weighted with lead to 26.5 pounds (12 kg), with

the center of gravity located approximately 6 in (15 cm) above the crotch.

This weight is the 90th percentile weight of a 14 month-old child (data

received from Dr. Richard Snyder, Univ. of Michigan). Several physicians

consulted agreed that this was an appropriate upper limit for children who

use walkers. The location of the center of gravity of the weighted doll was at the same location as the e.g. of a child. The doll was placed in

the walker during all dynamic stability tests, and restrained in approximately the same position as a child would use for that direction of motion,

i.e., sitting back for backward travel, leaning forward for forward travel.

The test setup for dynamic stability tests is shown in fig. 3. The

walker is placed on a flywood ramp at the height necessary to generate

the required test speed, as determined by trial runs, and restrained at

this position by a string. The wheels are alined in the direction of

intended motion, and the obstruction placed in the path of intended

motion far enough away from the ramp so that the walker will be com- pletely off the ramp before impact. The walker is released by burning

the string, impacts the obstruction, and either stops, rolls over the

obstruction, or tips over. Approximately ten replicate runs were taken

for each combination of parameters, and runs in which the walker rotated

(changed orientation) before impact were not considered good runs. Tests

with some combinations of parameters were not run if the results could be

logically anticipated. For example, if a series of forward runs at

6 ft/s (1.8 m/s) into a 1.0-in (2.5-cm) obstruction resulted in the

walker stopping, it was judged that runs at slower speeds into lower

obstructions would result in the walker stopping or rolling over the obstruction, both "passing" results, so the tests were not run. One result

was observed contradictory to this assumption, specimen 7 in the backwards orientation (see table 2) . This walker stopped after impacting

the 1-in (2.5-cm) barrier but tipped after impacting the 0.5-in (1.3-cm)

barrier. The geometry of this particular walker is such that the metal

rim impacted the 1-in (2.5-cm) barrier and prevented the walker from

tipping, while the rim went over the 0.5-in (1.3-cm) barrier, allowing

the wheels to impact it, and it tipped. No other walkers tested had a similar geometry.

The results of dynamic stability tests run on thirteen walkers and

walker-jumpers are given in tables 1-3. For all test situations,

replicate tests were run until at least 70 percent had the same result.

Note that only three of the items tested (specimen Nos. IIB, 12A, and

13) did not tip over with any combination of parameters, while one (specimen No. 7) tipped over with only one combination of parameters,

and another (specimen No. 9A) tipped with only two. All others tipped

with at least 4 out of the maximum of 18 combinations of parameters.

These tests simulate the walker running into raised barriers, but

there are other hazards, such as gravel at the end of driveways or heating vents in a floor, that may cause the walker to stop or tip. For

these situations, the results with 1-in (2.5-cm) barrier may be applicable,

3
since no walkers rolled over the obstruction. For this situation, for 6

combinations of parameters (2 speeds and 3 orientions) , four had no tips

and another had only one.

As a general rule, the walkers that did not tip or tipped the

fewest number of times were the ones with wider wheel bases and lower

centers of gravity.

2.2 Static Stability

It was felt that one source of possible accidents could involve

static stability, i.e., a child tipping the walker over from a standing

position and falling over on top of it. To prevent this, the length

from the seat crotch to the ground with the walker tipped to the un- stable equilibrium position must be greater than the child's leg length

(see fig. 4) . The dimensions for forward and sideways tip of thirteen

walkers are given in table 4. This data can be correlated with leg

length data when they become available to determine the safety of each

walker

2.3 Single-Step Roll-Over Tests

While it is probably impractical to expect a walker to go down a flight of stairs without tipping, there is some thought that it might

not be unreasonable to expect it to run off a single step without

tipping. This might provide some protection for occurrences such as running off a raised patio, into a sunken den or family room, etc.

The ramp for the dynamic stability test was placed on a 7. 8-in

(20-cm) high platform and tests run at two speeds, 2 and 4 feet per

second (0.6 and 1.2 m/s) , and the three orientations (see fig. 5). The

slower speeds were used because it was felt that the walker would be

more likely to tip at slower speeds. The results of these tests are given in table 5. None of the walkers passed the test for all com- binations of parameters.

2.4 Location of Scissor Joints

The shortest distances from the armpit of the doll seated in the

walkers to any exposed scissor joints were measured and are given. in

table 6. These data can be correlated with arm length data when they

become available to determine the safety of each walker.

2.5 Plastic Bead Strength

Several walkers have plastic beads within reach of the child's mouth

that could possibly break if bitten. The compressive breaking strengths

of these beads were determined and the lowest value and average value for

beads from each walker are given in table 7. All shattered into small

Jagged pieces. The average breaking force for the different types of
beads ranged from 27 to 490 Ibf (120 to 2180 N) . This lowest value would

seem to be within the biting force capability of a child.

2.6 Durability

To determine the ability of the walker-jumpers to withstand repeated

impacts, a canvas bag with 25 pounds (13 kg) of lead shot was dropped

repeatedly from a height of 2 in (0.5 cm) into the walker seat. Six

walker-jumpers were tested in this configuration, specimen numbers 1, 2,

9B, lOB, llA, and 12B. All withstood 10,000 cycles without any visable

damage. It should be noted that the cloth seat of specimen No. 5 ripped

during dynamic stability testing (see footnote a. Table 2) before it

could be tested for durability. An identical specimen could not be procured to determine if this model would have passed the durability test.

3. DISCUSSION

The tests run in this program were intended to simulate to some extent actual use conditions while keeping the test apparatus as simple

as possible. The only test for which any analytical correlation exists,

the dynamic stability test, showed good correlation between experimental

results and analytical prediction based on energy considerations as described earlier. This would indicate that this is a valid test method

for determining dynamic stability characteristics.

4. CONCLUSION

An analysis of hospital accident reports and inspection of available

walker-jumpers indicated probable and possible causes of injuries to

infants. The test methods were developed to determine the performance

characteristics of walkers, and to determine if the characteristics

leading to accidents are inherent to a given item. These test methods

and performance criteria can be used to aid in writing federal safety

standards

5
Table 1 - Results of Dynamic Stability Tests, Forward Orientation

Specimen

number

4 ft/s (1.2 m/s)

Obstruction Height

Speed

6 ft/s (1.8 m/s)

Obstruction Height

1

2

3

4

5

6

1

8

9A

IDA

IIB

12A

13

0.25 in

(0.6 cm)

R

R

R

R

T

R

R

R

0.5 in

(1.3 cm)

R

S

T

S

T

S

T

1.0 in

(2.5 cm)

S

S

T

S

T

S

S

T

0.25 in

(0.6 cm)

R

R

T

R

T

R

R

R

0.5 in

(1.3 cm)

R

S

T

S

T

S

S

T

1.0 in

(2.5 cm)

S

S

T

S

T

S

S

T

S

T

S

S

S

R - walker rolled over obstruction

S - walker impacted obstruction and stopped without tipping over

T - walker impacted obstruction and tipped over

6
Table 2 - Results of Dynamic Stability Tests, Backward Orientation

Speed

Specimen 4 ft/s (1.2 m/s) 6 ft/s (1.8 m/s)

number Obstruction Height Obstruction Height

0.25 in

(0.6 cm)

0.5 in

(1.3 cm)

1.0 in

(2.5 cm)

0.25 in

(0.6 cm)

0.5 in

(1.3 cm)

1.0 in

(2.5 cm)

1 R R S R T T

2 R T T R T T

3 R S S R T T

4 R S S R S S

5 (a) (a) (a) R T (a)

6 R S S R S S

7 R S S R T S

8 R T T R T T

9A S

lOA S S R T T

IIB S

12A S

13 S S

R - walker rolled over obstruction

S - walker impacted obstruction and stopped without tipping over

T - walker impacted obstruction and tipped over

(a) - During testing, a seam in the cloth seat of specimen number 5

completely separated so that it would no longer support the doll

so testing was discontinued.

7
Table 3 - Results of Dynamic Stability Tests, Sideways Orientation

Speed

Specimen 4 ft/s (1.2 m/s) 6 ft/s (1.8 m/s)

number Obstruction Height Obstruction Height

. 0.25 in

(0.6 cm)

0.5 in

(1.3 cm)

1.0 in

(2.5 cm)

0.25 in

(0.6 cm)

0.5 in

(1.3 cm)

1.0 in

(2.5 cm)

1 ^ R R S R T T

2 R s T R T T

3 R T R T T

4 R T T R T T

5 (a) fa") faY Ca") (a)

6 RJX T T R T TX

7 R s s R s s

8 R *? 1? T TX

9A R s R T T

lOA T s R T T

IIB S S

12A (b) (b) (b) (b) (b) (b)

13 R S S

walker rolled over obstruction

walker impacted obstruction and stopped without tipping over

T - walker impacted obstruction and tipped over

(a) - During testing, a seam in the cloth seat of specimen number 5 completely

separated so that it would no longer support the doll, so testing was discontinued.

(b) - The rear wheels of specimen number 12A were fixed so direct sideways

motion was impossible.

8
Table 4 - Seat Crotch to Floor Distance for Loaded Walkers

in the Unstable Equilibrium Position.

Specimen

number Forward Tip Sideways Tip

in cm in cm

1 10.5 26.7 7.8 19.8

2 12.2 31.0 7.8 19.8

3 9.8 24.9 9.8 24.9

4 11.6 29.5 9.0 22.9

5 (a) (a) (a) (a)

6 9.8 24.9 8.2 20.8

7 9.2 23.4 9.0 22.9

8 9.0 22.9 10.5 26,7

9A 10.0 25.4 6.8 17.3

lOA 10.6 26.9 8.2 20.8

IIB 10.6 26.9 9.0 22.9

12A 9.4 23.9 7.6 19.3

13 8.0 20.3 8.8 22.4

(a) Specimen damaged during previous testing.

9
I

Table 5 - Results of One-Step Roll-over Tests, Step Height 7.8 in (20 cm).

Specimen

number Forward Orientation Backward Orientation Sideways Orientation

2 ft/s

(0.6 m/s

4

) (1.

ft/s

2 m/s)

2 ft/s

(0.6 m/s)

4

(1.

ft/s

2 m/s)

2

(0.

ft/s

.6 m/s)

4 ft/s

(1.2 m/s)

1 R R T T T T

2 . R R T T T

3 T T

" T . , T T T

4 R R R T T

5 (a) (a) (a) ; (a) (a) (a)

6 (a) (a) (a) (a) (a)

7 T T T T T

8 : t T T T T

9A R R I s T T T

lOA T T T T T

IIB R R T R T R

12A R R R (b) (b)

13 T T T T T T

T - walker tipped over

R - walker rolled over step without tipping

(a) - walker damaged in previous tests

(b) - fixed wheels prevented sideways motion

10
Table 6 - Distances from Armpit to Exposed Scissor Joints in Walker

Jumpers

Specimen

number Distance to Scissor Joint

in cm

1 4.2 10.7

2 5.0 12.7

3 6.5 16.5

4 4.5 11.4

5 (a) (a)

6 (b) (b)

7 (b) (b)

8 (b) (b)

9A 4.0 10.2

lOA (b) (b)

IIB 9.0 22.9

12A 4.0 10.2

13 (b) (b)

(a) - specimen broken during previous tests

(b) - no exposed scissor joints

11
Table 7 - Compressive Breaking Strengths of Plastics Beads

from Walkers

Specimen Minimum Breaking Average Breaking

Number Strength Strength

Ibf N Ibf N

1 323 1440 344 1530

2 296 1320 311 1380

3 190 845 190 845

4 97 431 100 445

6 27 120 27 120

7 331 1470 344 1530

8 479 2130 490 2180

12



I






NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. Bibliographic data

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1. PUBLICATION OR RKPORT NO.

NBSIR 74-434

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTI I LE 5. Publication Date

Test and Evaluation of Baby Walkers and Walker-Jumpers 6. Performing Organization Code

y. AUTHOR(S)

Daniel J. Chwirut

8. Performing Organ. Report No. NBSIR 74-434

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/»'ork Unit No. 2130449

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

13. Type of Report & Period Covered

Final

14. Spoftsoring Agency Code

15. SUPPLEMENTARY NOTES

\6. ABSTRACT (A 200- word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) Accident reports from hospital emergency rooms were surveyed to determine the

probable causes of accidents involving baby walkers and walker-jumpers. Test methods

%jere developed to simulate service conditions to determine if the characteristics

leading to accidents are present in all or only a few of the items on the market. These

test methods include tests for dynamic and static stability, step roll-over stability plastic bead strength, durability, and location of scissor joints. The test methods

and performance criteria are intencied to supply information leading to federal

safety standards.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Accident reports; baby walkers; infants; safety standards; test methods; walker -jumpers.

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